Nickel-Catalyzed Highly Enantioselective Hydrogenation of β-Acetylamino Vinylsulfones: Access to Chiral β-Amido Sulfones

Article abstract of DOI:10.1021/acs.orglett.8b02579

The nickel/(S)-Binapine complex was found to be an efficient catalyst for asymmetric hydrogenation of β-acetylamino vinylsulfones to afford chiral β-Amido sulfones with excellent yields and enantioselectivities (up to 95% yields and >99% ee). This protocol has good compatibility with a series of substituted (Z)-β-acetylamino vinylsulfones or Z/E isomeric mixtures. A gram-scale reaction has also been achieved in the presence of a 0.2 mol % catalyst loading.

Full text of DOI:10.1021/acs.orglett.8b02579

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Nickel-Catalyzed Highly Enantioselective Hydrogenation of
β‑Acetylamino Vinylsulfones: Access to Chiral β‑Amido Sulfones
Jiao Long,† Wenchao Gao,† Yuqing Guan,† Hui Lv,*,†,§ and Xumu Zhang‡
†Key Laboratory of Biomedical Polymers of Ministry of Education & College of Chemistry and Molecular Sciences, Engineering
Research Center of Organosilicon Compounds & Materials, Ministry of Education, Wuhan University, Wuhan, Hubei 430072,
China
‡Department of Chemistry and Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen, Guangdong
518055, China
§Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of
Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China
S
* Supporting Information
ABSTRACT: The nickel/(S)-Binapine complex was found to be an
efficient catalyst for asymmetric hydrogenation of β-acetylamino vinyl-
sulfones to afford chiral β-Amido sulfones with excellent yields and
enantioselectivities (up to 95% yields and >99% ee). This protocol has
good compatibility with a series of substituted (Z)-β-acetylamino
vinylsulfones or Z/E isomeric mixtures. A gram-scale reaction has also
been achieved in the presence of a 0.2 mol % catalyst loading.
wing to its perfect atom economy and high efficiency,
Otransition-metal-catalyzed asymmetric hydrogenation has
been considered one of the most powerful tools for the synthesis
of chiral molecules.1 In past decades, asymmetric hydrogenation
has been intensively investigated and remarkable progress has
been made in both academic research and industrial
application.2 However, traditional research on asymmetric
hydrogenation is focused on noble transition metal catalysts
based on Ru, Rh, Ir, or Pd,1,2 which unavoidably suffer from
some inherent drawbacks of the precious metal catalyst, such as
being expensive, toxic, and environmentally harmful. Therefore,
first-row transition-metal-catalyzed asymmetric hydrogenation
has drawn a great deal of attention due to its potential
advantages in cost and sustainability.3 In this context, Hamada,4
Zhou,5 and Chirik6 reported their pioneering work in nickel-
catalyzed asymmetric (transfer) hydrogenation, greatly promot-
ing the development of nickel-catalyzed asymmetric hydro-
genation. Although Ni-catalyzed asymmetric hydrogenation of
alkenes,5a−c,6 ketones,4,7 enamides,5a imines,5e and hydrazo-
nes5d,e have been achieved, Ni-catalyzed asymmetric hydro-
genation is still in its infancy, and exploiting a new catalytic
system which can work as well as (or even better than) the
precious-metal-catalyzed system is highly desirable.
Figure 1. Examples of bioactive molecules containing β-amido sulfone
scaffolds.
high yield and good to excellent ee.11 However, the substrate
scope of this reaction is limited to (Z)-aryl substituted β-amido
sulfones, alkyl substituted β-amido sulfones, and a Z/E isomeric
mixture of β-amido vinylsulfones which gave the target products
with poor enantioselectivity (Scheme 1, eq 1). To develop a
general method for asymmetric hydrogenation of β-acylamino
vinylsulfones with a broad substrate scope including both a Z/E
isomeric mixture and alkyl substituted β-acylamino vinyl-
sulfones is still a problematic issue. Recently, our group achieved
nickel-catalyzed asymmetric hydrogenation of β-acylamino
nitroolefins12 and β-acylaminoacrylates13 and found that a
nickel catalytic system has good substrate compatibility.
Inspired by these result, we envision that nickel-catalyzed
asymmetric hydrogenation of β-acylamino vinylsulfones may be
Chiral β-amino sulfones are privileged motifs occurring in
many natural products and biologically active compounds
(Figure 1).8 Thus, great efforts have been made for the synthesis
of β-amino sulfones, and a variety of approaches have been
developed. The typical methods include asymmetric aza-
Michael additions to α,β-unsaturated sulfones9 and stereo-
selective additions of sulfonyl carbanions to chiral N-sulfinyl
imines.10 In 2014, Zhang and co-worker reported Rh-catalyzed
asymmetric hydrogenation of β-acylamino vinylsulfones with a
Received: August 11, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b02579
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Asymmetric Hydrogenation of Sulfones
Table 2. Ligands Screening for the Ni-Catalyzed Asymmetric
Hydrogenation of 1a
a
b
c
entry
ligand
(S)-BINAP
(S,S)-Me-DuPhos
(S,S)-Et-DuPhos
(Rc,Sp)-DuanPhos
(S)-SegPhos
(S)-DTBM-SegPhos
(S)-Binapine
(S,S)-f- Binaphane
(S,S)-Ph-BPE
conv (%)
yield (%)
ee (%)
1
2
3
4
5
6
7
8
52
27
24
>99
63
<5
−
−
−
−
−
−
99
−
−
−
−
−
99
99
−
trace
trace
10
trace
<5
48
>99
<5
33
<5
<5
53
90
81
trace
88
Table 1. Solvent Screening for the Ni-Catalyzed Asymmetric
a
−
Hydrogenation of 1a
9
trace
10
11
12
13
14
(R)-Walphos
−
−
(R)-TaniaPhos
(R,S)-t-Bu-JosiPhos
(S)-Binapine
(S)-Binapine
(S)-Binapine
<5
79
72
d
e
f
15
−
b
c
entry
solvent
MeOH
EtOH
conv (%)
yield (%)
ee (%)
a
Unless otherwise noted, all reactions were carried out with a
1
2
3
4
5
6
7
8
9
>99
>99
trace
>99
>99
trace
trace
trace
trace
trace
>99
trace
trace
−
69
67
−
−
−
−
−
−
−
−
99
99
−
−
−
Ni(OAc)2/ligand/substrate (0.05 mmol) ratio of 1:1.1:20 in 1 mL of
b
solvent at 50 °C under H2 (50 atm) for 12 h. Yield was determined
iPrOH
1
by H NMR analysis, using 1,3,5-trimethoxybenzene as the internal
c
CF3CH2OH
(CF3)2CHOH
toluene
THF
CH2Cl2
EtOAc
CH3CN
CF3CH2OH
standard. Determined by HPLC analysis using a chiral stationary
d
e
f
phase. Hydrogen pressure was 20 atm. Reaction time was 8 h. At
room temperature.
−
−
99
10
11
d
88
a
Unless otherwise noted, all reactions were carried out with a
Ni(OAc)2/(S)-Binapine/substrate (0.05 mmol) ratio of 1:1.1:20 in 1
mL of solvent at 50 °C under H2 (50 atm) for 12 h. The catalyst was
prepared beforehand with a mixture of methanol and tetrahydrofuran
(in a 1:1 volume ratio) at room temperature for 1 h in a nitrogen-
b
1
filled glovebox. Yield was determined by H NMR analysis, using
c
1,3,5-trimethoxybenzene as the internal standard. Determined by
HPLC analysis using a chiral stationary phase. The slovent contains
d
10% methanol.
potentially efficient to access to chiral β-amino sulfones. Herein,
we report the first nickel-catalyzed asymmetric hydrogenation of
β-acylamino vinylsulfones with high yields, excellent enantiose-
lectivities, and good substrate tolerance (Scheme 1, eq 2).
We began the initial investigation with the asymmetric
hydrogenation of β-acetylamino vinylsulfones 1a to optimize the
reaction conditions. A variety of solvents were examined when
the reaction was carried out in the presence of 5 mol %
Ni(OAc)2 at 50 °C under 50 atm of H2. As shown in Table 1, the
exploration of various solvents indicated that CF3CH2OH is a
good solvent for this reaction, generating target product 2a with
moderate yield and excellent enantioselectivity (Table 1, entry
4). A similar result can be achieved with hexafluoroisopropanol,
giving chiral β-amido sulfone 2a with a 67% yield and 99% ee
(Table 1, entry 5). However, when iPrOH and nonprotonic
solvents toluene, THF, CH2Cl2, EtOAc, and CH3CN were used,
only trace conversions were detected (Table 1, entries 3, 6−10).
Although MeOH and EtOH afforded full conversions, mixed
Figure 2. Structures of the phosphine ligands for hydrogenation of β-
acetylamino acrylosulfones 1.
systems containing a N-(1-phenylethyl)acetamide byproduct
were detected with no target product (Table 1, entries 1−2).
According to the above results, we speculated that methanol and
tetrahydrofuran may inhibit the formation of the target product.
However, methanol is indispensable in the system because
nickel acetate is hardly soluble in other solvents, and ligand has
good solubility in tetrahydrofuran. Therefore, we adjusted the
ratio of methanol, tetrahydrofuran, and trifluoroethanol and
screened a series of mixed solvents (see Supporting Information,
Table S2). When the reaction was conducted in a mixed solvent
B
DOI: 10.1021/acs.orglett.8b02579
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
of methanol and trifluoroethanol with a 1:9 volume ratio, the
best result was obtained, affording chiral β-amido sulfone 2a
with a 88% yield and 99% ee (Table 1, entry 11).
Scheme 2. Substrate Scope of Ni-Catalyzed Asymmetric
Hydrogenation of β-Acetylamino Acrylosulfones
a
Subsequently, a variety of diphosphine ligands (Figure 2)
were evaluated, and the results reveal that (S)-Binapine is
superior to all the other ligands tested, giving chiral β-amido
sulfone 2a with 88% yield and 99% ee (Table 2, entry 2). Most of
the other diphosphine ligands, whether they were P chiral
ligands, planar chiral phosphine ligands, or phosphine ligands
with a chiral center, failed to give the target product (Table 2,
entries 1−12). When the reaction was conducted with a lower
hydrogen pressure or shorter reaction time, the yield dropped
slightly, but without any loss in enantioselectivity (Table 2,
entries 13−14). The reaction was totally inhibited when the
temperature was decreased to room temperature (Table 2, entry
15).
With the optimal conditions in hand, the substrate scope of
this reaction was investigated. As shown in Scheme 2, the
reaction exhibited good tolerance to the substrates, and various
β-aryl substituted β-acylamino vinylsulfones could be hydro-
genated very efficiently, giving β-acylamino sulfones with good
yields and excellent enantioselectivities (2a−2k). When R1 was
changed to a heteroaryl group, the reaction proceeded smoothly,
albeit the yield decreased slightly (2l). Replacing R2 by a phenyl
group, the yield increased slightly while the enantioselectivity
remained the same (2m). It is worth noting that β-alkyl
substituted β-acylamino vinylsulfones, poor substrates for
rhodium-catalyzed asymmetric hydrogenation, are well toler-
ated in the nickel-catalyzed system (2n and 2o).
To demonstrate the potential utility of this methodology, the
Z/E mixture (1:1) of 1m was used directly to investigate the
compatibility of this catalytic system. Fortunately, the Z/E
isomeric mixture of β-amido sulfones, a kind of incompatible
substrate for rhodium catalytic system,11 proceeded very
smoothly in the nickel/(S)-Binapine catalytic system, giving
the desired product in 85% yield with 97% ee (Scheme 3, eq 1).
In addition, the asymmetric hydrogenation of (Z)-1m was
conducted on a gram scale in the presence of a 0.2 mol % catalyst
loading, affording 2m in 90% yield with unchanged
enantioselectivity (99% ee) (Scheme 3, eq 2). These results
declare that the nickel/(S)-Binapine catalytic system can work
as well as or even better than the Rh-catalyzed system on the
compatibility of Z/E mixtures and alkyl substituted β-amido
sulfones.
In conclusion, nickel-catalyzed asymmetric hydrogenation of
β-acylamino vinylsulfones has been achieved, affording β-
acylamino sulfones with high yields and excellent enantiose-
lectivities. This protocol provides an efficient access to chiral β-
amido sulfones. More importantly, the Ni(OAc)2/(S)-Binapine
catalytic system exhibited better performance than the precious
catalyst in asymmetric hydrogenation of alkyl substituted β-
acylamino vinylsulfones and in asymmetric hydrogenation of the
Z/E mixture of β-acylamino vinylsulfones. Further investiga-
tions on nickel-catalyzed asymmetric hydrogenation are under-
way in our laboratory.
a
All reactions were carried out with a Ni(OAc)2/(S)-Binapine/
substrate (0.2 mmol) ratio of 1:1.1:20 in 1 mL of mixture solvents
(MeOH/CF3CH2OH = 1:9) at 50 °C under H2 (50 atm) for 12 h. All
yields were isolated yields. Enantiomeric excess was determined by
HPLC analysis using a chiral stationary phase.
Scheme 3. Gram-Scale Reaction and S/C Evaluation
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.8b02579.
Experimental details and characterization data (PDF)
C
DOI: 10.1021/acs.orglett.8b02579
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: huilv@whu.edu.cn.
ORCID
(5) (a) Yang, P.; Xu, H.; Zhou, J. Angew. Chem., Int. Ed. 2014, 53,
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Hui Lv: 0000-0003-1378-1945
Notes
The authors declare no competing financial interest.
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We are grateful for financial support from the National Natural
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21432007), the Natural Science Foundation of Hubei Province
(2018CFB430), the Fundamental Research Funds for the
Central Universities (2042017kf0177), the Important Sci-Tech
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